The present invention relates to the field of optical gyroscopes. More specifically, the invention relates to the magnetic shielding of an optical gyroscope.
A key performance parameter for optical gyroscopes, such as fiber optic and similar optic gyroscopes used for inertial sensing, is bias sensitivity to magnetic fields. Sources of magnetic flux include the Earth""s magnetic field, electrical machinery, etc. For a fiber gyroscope used in inertial navigation systems, the allowable magnetic sensitivity of the instrument bias is between 0.001 and 0.0001 degree per hour per guass (deg/hr/guass). The inherent sensitivity of an unshielded gyroscope is 1 deg/hr/gauss.
The most effective method to reduce the bias sensitivity to magnetic field is to reduce the magnitude of the local field by the addition of a magnetically shielding structure (xe2x80x9cmagnetic shieldxe2x80x9d) around the optics. Magnetic shields are made of a high permeability shielding material that will function as a preferred path for an ambient field. Essentially, the magnetic shield creates a high-permeability path for the magnetic field in order to reroute the magnetic field around the optical gyroscope inside the shield, thereby reducing the effect on bias.
Performance of the magnetic shield is determined by the overall size, shape, and composition of the container, as well as magnitude of the ambient field. One variable included in the size and shape, is the number of distinct layers of shielding material present in the shield. These layers are separated from each other by a non-magnetic material or by a vacancy. One variable which affects the performance of a multi-layered shield is the size of this gap between the shield layers. Another performance variable is the mating method of multi-piece shield.
Presently, magnetic shields are usually two-piece assemblies, namely a lid and a base, where one piece overlaps the other. This overlapping results in the inside layer of the lid mating on the outside surface of the outer layer of the base. This overlap creates a discontinuity in the ambient field paths created by each shielding layer. Thus, the result is not a true multi-layered shielding effect since there are not separate paths that the magnetic field lines can travel.
Accordingly, it is desirable to provide a magnetic shield having a multiple-layered lid and a multiple layered base, wherein each layer of the lid is aligned with the corresponding layer of the base to create a continuous multi-layered shield throughout the joint of the lid and the base of the shield. The present invention provides such a mated shield with a true multi-layered shielding effect, which results in improved suppression of the magnetic field surrounding the gyroscope.
It is further desirable to provide an alignment mechanism to maintain the mating of the lid and the base of a magnetic shield while the shield is in use. The present invention provides such an alignment mechanism. In the present invention, the alignment mechanism ensures that the continuous ambient fields created by the layers of a shield will not be disrupted during the use of a gyroscope.
The present invention provides a magnetic shield having a multiple-layered lid and a multiple layered base, wherein each layer of the lid is aligned with the corresponding layer of the base. The present invention also provides an alignment mechanism to maintain the alignment of the corresponding layers of the lid and the base of the shield.